1. Field of the Invention
The present invention relates to a composition and method for coating an object of interest, and more particularly to a composition which may be applied to metal or other heat resistant substrates; the composition when properly applied providing a durable and attractive finish, while simultaneously imparting improved corrosion resistance to the object of interest, and further having no deleterious environmental impact.
2. Description of the Prior Art
The prior art is replete with numerous compositions and methods for coating objects of interest such as steel, or aluminum assemblies, and wherein the coating composition is applied to the object of interest to substantially impede corrosion which acts at the surface of the object, following its exposure to various corrosive substances which are present in the ambient environment--such as atmospheric gases, water, and the like. For example, and in the production of steel, and in particular steel which has a predetermined hardness, the surface of the steel may often become so reduced by the processing steps that the surface of the steel will corrode rapidly (often in minutes) when exposed to ambient water vapor. To address this particular problem, manufacturers of steel often apply a coating of soluble oil to the steel being processed thereby providing a surface which will impede, at least for some period of time, the onset of corrosion.
Additionally, among the various metallic coatings applied to iron and steel which provide protection against corrosion, zinc has played a very important role. In this regard, the process of applying a zinc coating is considered to be the technique of galvanizing. Galvanizing is used extensively for such products as bar, tube, strip wire, and sheet stock, and for all manner of articles and utensils such as buckets, watering cans, garbage cans, etc.
The most commonly applied process of galvanizing is "hot dip" galvanizing whereby the zinc coating is obtained by the immersion of the object of interest in a bath of molten zinc. In this process, the zinc combines with, for example, iron so that iron and zinc alloy crystals are formed, which provide a firmly adhered coating.
To employ a successful hot dip galvanizing method, the object to be exposed, such as steel must be substantially free of all oil, grease, dirt, scale, and corrosion products. The preparatory treatment may include degreasing with a suitable solvent, pickling with acid, rinsing the object, treating it with a flux, and drying. The purpose behind the step of pickling is to remove any oxide films which are present at the surface by the action of hydrochloric or sulfuric acid. The flux, which is usually a mixture of zinc chloride and ammonium chloride, serves to remove any remaining traces of impurities and increases the wetability of the steel surface.
In "wet galvanizing", the flux is deposited in molten form in the zinc bath, and the metal to be galvanized is introduced into the bath through the layer of flux. In "dry galvanizing", the metal components are first dipped in a solution of the flux and are then dried so that they become precoated with a thin film of flux which melts in the zinc bath.
Another commonly employed method for applying protective coatings to metal surfaces includes metal spraying. In this particular process, molten metal is applied on the surface of the object to be coated. Normally the coating metal, which is in the form of a wire, is fed into a spray gun or similar device whereby it is melted by the combustion of a fuel gas such as, for example, a mixture of oxygen and acetylene. Normally, the spray gun, or other spray assembly, includes two rollers which are powered by an air turbine, and which feeds the wire through the central portion of a special nozzle. In this nozzle the gas is ignited, and the wire is melted and thereby emerges from the nozzle in a particulate form. The molten metal is thereafter atomized by compressed air and is projected at high velocity against the surface to be coated. Coatings of lead, aluminum, silver or stainless steel are often used for providing protection against corrosion for special apparatuses employed in the chemical and food stuff industries. Steel or hard-alloy coatings are also used as wear surfaces on various objects. For instance, light alloy pistons can be coated with a sprayed steel coating. In the electronics and telecommunications industries, metallic coatings are applied to nonmetallic materials to make them electrically conductive.
Another common method employed for coating surfaces to inhibit corrosion includes the process of electroplating. Electroplating is the process of producing a metallic coating on a surface by electro-deposition, that is, by the action of an electric current. Such coatings may perform a mainly protective function, that is, to prevent corrosion as for example plating with zinc, or electro-galvanizing with tin; or further, a decorative function such as applying gold or silver plating. The principle surrounding electroplating is that the coating metal is deposited from an electrolyte, that is, from an aqueous acid or alkaline solution onto the object.
To obtain an acceptable and firmly adhering electroplated coating, it is necessary to subject the objects to be coated to a thorough cleaning. This may be achieved by a mechanical treatment, that is, sandblasting, grinding, wire brushing, scraping or the like, or by physical methods such as degreasing with organic solvents or by chemical methods such as pickling with acid or degreasing by the action of alkalines (this is often termed "saponification"), or by electrocleaning which is a method of cleaning by electrolytic action. In this regard, electrolytic action is often described as the scrubbing action which is expressed by the evolution of gas at the surface of the metal. Additionally, wetting agents and emulsifiers may be added and are useful to the process.
While the several processes noted above operate with some degree of success, they have a number of shortcomings which have detracted from their usefulness. For example, many of the processes noted above include the use of compositions which are not environmentally friendly, that is, they include compositions having heavy metals or VOC's (volatile organic compounds) which have been identified as being harmful to the environment or which are otherwise prohibited or regulated by various state and federal laws such as California Proposition 65. Additionally, common methods such as the zinc electroplating method, discussed earlier, and which will normally produce an object which has a level of corrosion resistance equal to approximately 250 hours when exposed to a salt spray, are often further enhanced by other compositions which are applied thereto and which extend their corrosion resistance. For example, a second coating termed an "E coating" (electrolytic coating) is often applied to zinc electroplated objects in order to enhance their corrosion resistance. Normally, it is expected that an E coating may add approximately another 100 hours of corrosion resistance to these objects. Additionally, a zinc-nickel coating may also be applied to an object by the same method, and this process may increase the corrosion resistance of this same part to a period of approximately 900 to 1,000 hours when exposed to the same corrosive conditions.
Another shortcoming attendant to the prior art processes is that each of these processes require that the object be thoroughly cleaned prior to the plating process, thereby ensuring that a uniform surface be applied to same. The extra steps required to clean the object, for example, are often time consuming, costly, and further include the use of various solvents and other materials which are, as discussed above, prohibited or regulated by public law, or alternatively, are difficult to dispose of in an environmentally safe manner.
In addition to the foregoing, and while these various methods, as earlier discussed, have produced various laudable benefits, they have a further shortcoming inasmuch as they cannot be readily retrofitted or introduced into a manufacturing process without substantially interfering or delaying the process, and further cannot normally be introduced without substantial expense.
Therefore, it has long been known that it would be desirable to have a composition and method for coating an object of interest and which has particular utility when applied to objects of interest which corrode when exposed to water vapor and other corrosive substances in the ambient environment, and which further, can be readily introduced into the manufacturing process, and which produces a corrosion-resistant surface which is durable, and attractive, and which substantially avoids the shortcomings attendant with the prior art practices.